Heterogeneity is a hallmark of tumors and has a crucial role in the outcome of the malignancy, because it not only confounds diagnosis, but also challenges the design of effective therapies. Much attention has been placed on tumors as architecturally heterogeneous systems that differ regionally in vasculature, host infiltrates, and connective tissue components, but far less is known about bioenergetic heterogeneity and how cancer cells dependent on different bioenergetic pathways interact together to drive tumor growth. In this application, we propose to test the hypothesis that glycolytic chemosensitive glioma cells inhibit the expansion and growth of Oxphos-dependent chemoresistant glioma cells through a paracrine mechanism involving secreted insulin growth factor binding protein 6 (IGFBP6). Two aims are proposed to: 1) Characterize the paracrine pathway between glycolytic chemosensitive cells and Oxphos- dependent chemoresistant cells, and 2) Determine the effect of TMZ treatment on the enrichment of Oxphos-dependent chemoresistant cells. In both aims, we will use genetic and pharmacologic approaches in human cell lines and patient?derived xenoline models. The work proposed is expected to identify a novel paracrine pathway between Oxphos-dependent chemoresistant and glycolytic chemosensitive glioma cells and demonstrate that standard of care TMZ, by interrupting this paracrine regulation, expands the pool of chemoresistant cells, leading to increased tumorigenicity. If successful, this study will define a novel tumor growth model where by intratumoral bioenergetic heterogeneity is critically involved in the growth of the tumor as a whole. Importantly, we propose that standard treatment modalities may selectively destroy this structured population and facilitate subsequent progression. Consequently, controlling tumor progression by maintaining rather than destroying this suppressive tumor layer may be more effective than conventional high-dose density therapy that aims to kill the maximum possible number of tumor cells.